Condensation damp: thermal bridges

When and why does so-called condensation damp form in some rooms of a home? What counts as a thermal bridge? How can they be avoided? Below we will try to answer these questions, which come up so often when these troublesome defects appear.

Condensation damp is the result of water vapour being retained in the capillaries of walls or wall coverings because of the difference between the indoor and outdoor temperature. Condensation is caused by the temperature difference between a warm interior and the cold exterior, and is channelled through so-called “thermal bridges”. This contrast causes excess water vapour in the air to condense. It usually shows up as colonies of mould (black stains), as small droplets (as if the wall were sweating) or as “blistering” paint.

This type of defect is usually caused by thermal bridges, which are areas through which heat is transmitted more easily, because they are made of a different material or thickness. A simple example would be a screw joining two wooden boards. As the screw conducts heat better than the wood, heat “escapes” through it. For this reason, before improving the performance of the rest of the insulation, you should consider eliminating the heat loss through the screw.

This is also why thermal bridges occur in building façades, where structural elements are in contact with the outside. For example, in a building with a steel or concrete frame, the columns and beams will act as a thermal bridge in relation to the masonry, which is normally brick or hollow concrete blocks. Masonry interrupted by a column or beam will have a thermal bridge in that area, because the column or beam transmits heat better, causing heat loss and creating a “cold spot” that can lead to condensation. Defects (damp patches with mould) can generally be seen at these thermal bridges. To prevent this heat transfer, what is known as a thermal break is used. It consists of preventing the inner and outer faces from touching each other by inserting a poor conductor between them, which greatly reduces heat loss

A common way of dealing with this frequent thermal bridge at the construction stage is not to place the columns or beams flush with the outer face of the façade, but set back a few centimetres from the masonry, enough to “protect” them with external thermal insulation. This would prevent troublesome condensation and the appearance of damp and mould inside homes. And that is how all buildings should be designed and built. If your home has condensation damp and you think it may have thermal bridges, consult us, and we will send one of our experts to check it properly.